During the process of refining a hot metal or an iron alloy, an oxidizing gas, mostly pure oxygen, is used. The oxygen is injected or blown from above onto a liquid metal bath in a metallurgical vessel, and it is of the utmost importance to be able to modify or vary the characteristics of the stream of the oxidizing gas, as well as its impact point on the surface of the bath, all depending on the state of progression of the refining process. This is all the more true since modern refining technologies use supersonic primary jets for oxidizing gas.
The design of a gas blowing lance, which is used in connection with a refining process of the kind described herebefore, is a rather intricate, matter. Indeed, the oxidizing gas must be able to react with the metallic bath to allow reactions like the decarburization of the iron to take place, and it must also be able to guarantee a post-combustion above the surface of the bath of the carbon monoxide generated as a result of the decarburization reaction. In addition the flow rate, i.e. the volume per unit time, of the oxidizing gas blown into the vessel must be regulated independently from the jet velocity of the gas. Moreover it is desireable to move the location where the gas jet impinges on the bath across the surface of the bath during the refining operation. This enlarges the area where the metallurgical reactions take place and intensifies the bath mixing effect of the jet. Also, the oxygen for post-combustion must be spread out over the most extended possible reaction area on the surface of the bath, while at the same time it must be guaranteed that the post-combustion of the carbon monoxide takes place in proximity to the surface of the bath and not in the upper parts of the vessel where the liberated energy could create a risk for the lance and/or the vessel mouth.
Luxembourg Patent No. 86 322 (corresponding to U.S. Pat. No. 4,730,784, both of which are assigned to the assignee hereof and are fully incorporated herein by reference thereto) relates to a nozzle of an oxygen blowing lance which allows for independent regulation of the exit velocity (Mach number) and the flow rate of the oxygen stream. A later development of such a refining lance, which has been disclosed in Luxembourg Patent No. 87 353 (corresponding to U.S. Pat. No. 4,993,691, both of which are assigned to assignee hereof and fully incorporated herein by reference thereto), makes it possible for the operator to vary, as a function of the different refining phases, the quantity of the primary oxygen supplied to the bath, while simultaneously imposing the required optimal shape and velocity on the oxygen jet. According to the device in U.S. Pat. No. 4,993,691 the refining lance is equipped with a nozzle to shape and to guide the primary oxygen jet. This nozzle comprises a conduit with a variable cross section which defines first a converging passage, then a throat passage and finally a diverging passage. The nozzle comprises a central body which is movable along the axis of the nozzle at the level of the throat. This central body has the shape of a substantially cylindrical body part followed by a nose streamlining in a concave way towards a conical point. By moving this central body, the free cross section of the throat and the shape of the divergent passage can be modified, and, as a consequence hereof, the characteristics of the nozzle can be continuously adjusted.
Luxembourg Patent No. 86 321 (corresponding to U.S. Pat. No. 4,730,813, both of which are assigned to the assignee hereof and are fully incorporated herein by reference thereto) discloses a device which, in conjuction with an oxygen top blowing refining lance, allows the oxygen jet coming out of the head of the lance to be deviated, within given limits, with respect to the axis of the lance and may thus be directed onto various impact points on the surface of the liquid bath to be refined. The device in said U.S. Pat. No. 4,730,813 includes a chamber having substantially the shape of a truncated pear in the vicinity of the outlet of the lance head. Through the action of gas jets in the vicinity of the outlet level of the nozzle which impinge laterally on the main jet of primary oxygen leaving the nozzle, the main jet is deviated towards one side of the pear-shaped chamber and moves along the walls of the chamber on the opposite side from where the lateral deviating jets originate. This causes the oxygen stream, which is at supersonic speed, to exit from the outlet of the lance head at a given angle with respect to the axis of the lance. The angle of deviation of the oxygen stream depends to a large extent on the shape of the wall of the chamber. By providing several orifices for the lateral gas jets and by directing the jets one after the other against the main refining gas stream, the impact point of this stream on the surface of the metal bath can be shifted along the circumference of a circle, and, depending on the position of the lateral jets responsible for the deviation, it can also be directed towards defined places on the surface of the bath.
Although it is thus possible to deviate the supersonic main refining oxygen stream, the lance is subject to important lateral reaction forces which strain the suspension and anchorage points of the lance body to such an extent that it becomes difficult in practice to figure out a reliable solution to these holding device related problems. Moreover the device of U.S. Pat. No. 4,730,813 only allows deviating the main stream of primary oxygen jet to some well defined specific places corresponding to the orifices of the lateral deviating jets.